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New Zealand has pulled off a major diplomatic coup by securing the support of 25 countries - including an initially reluctant Russia - to create the world's largest marine sanctuary.

The marine protected area (MPA) in the Ross Sea, north of Antarctica, was jointly devised by New Zealand and the United States and will cover 1.55 million square kilometres of prized ocean. Roughly the size of France, it will be the world's largest marine reserve.

"New Zealand has played a leading role in reaching this agreement which makes a significant contribution to global marine protection," Foreign Affairs Minister McCully said today.

Agreement on the MPA was reached following talks at the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) in Hobart this week.

The MPA is one of New Zealand's major foreign policy objectives, and it has taken six years of diplomatic wrangling to get all 25 countries which govern the Antarctic to agree to the proposal.

CCAMLR decisions require a consensus, and proposals can fail if any single country objects. Previous attempts to reach agreement have been scuppered by opposition from fishing countries, mainly Russia and Ukraine.

McCully lobbied his Russian counterpart Sergei Lavrov on the issue during a recent trip to Moscow.

United States Secretary of State John Kerry - who has a strong interest in marine protected areas - also played a role in convincing Russia of the merits of the MPA.

McCully underlined the significance of getting Russia to agree with a US-backed initiative during a low point in the two countries' relations because of conflicts in the Middle East.

"At a time when relations on so many fronts are difficult with the Russians, some co-operation and a constructive dialogue is very pleasing to us," he said.

The NZ-US proposal required some changes to secure the unanimous support of all member countries. The final agreement balanced marine protection, sustainable fishing and science interests, McCully said.

The Ross Sea is considered the last remaining pristine ecosystem on the planet, earning it the label "The Last Ocean". It is home to penguins, Antarctic toothfish, whales, and Weddell seals.

One of the groups which has lobbied hard for the MPA, the Antarctic Ocean Alliance, described the agreement as "momentous".

"CCAMLR made history today by declaring the world's largest marine protected area in the Ross Sea, protecting penguins, seals, whales and countless other creatures," spokeswoman Andrew Kavanagh said.

"This would not have been possible without Russia joining with other countries to achieve today's historic decision to protect the Ross Sea. The governments of the United States and New Zealand should also be commended for their tireless work these past six years."

Philippa Ross, the great-great-great-granddaughter of explorer Sir James Ross, was overwhelmed with emotion when contacted by the Herald today.

"It's massive," said Ross, who visited the Ross Sea with her uncle in February.

"I always held hope in my heart, and it had been a promising last couple of weeks - I know how much work has been done behind the scenes."

Ross hoped people were starting to realise that humankind should have no reign over nature.

Mike Walker, project director of the Antarctic Ocean Alliance, said the deal was an important milestone for ocean conservation, but urged countries to go further.

"For the first time, countries have put aside their differences to protect a large area of the Southern Ocean and international waters," he said.

"The limited 35-year restriction for protection of the Ross Sea contradicts the scientific advice that marine protection should be long-term.

"Nevertheless, we are confident that the significant benefits of protecting the Southern Ocean will soon be clear and the international community will act to safeguard this special place long into the future."

A group of emperor penguins on an ice float in the Ross Sea, Antarctica. Photo: John Weller

The new sanctuary could mean New Zealand is required to increase its monitoring of the Antarctic region for illegal fishing. The Royal New Zealand Navy conducts annual patrols of the Southern Ocean.

McCully said any decisions about monitoring would be made at a later date.

The MPA would also have an impact on the science New Zealand is carrying out in Antarctica.

McCully said New Zealand's Scott Base is due to be modernised, and the MPA could provide the motivation for a "contemporary science base".

"This MPA will obviously ask for more science work to be done down there as part of the research process."